A light source unit for a vehicle lamp is disclosed in, e.g., Japanese Patent Application Laid-Open No. 2003-317513 including a reflector having a first reflective surface inside a member having a substantially ellipsoid-of-revolution shape centering on an optical axis extending in the front and back directions of the vehicle, an LED disposed at a first focus at a vertical cross section of the first reflective surface, a projector lens disposed on the optical axis in front of the reflector, and a light control member provided between the LED and the projector lens. The light control member includes a fore-end edge disposed to pass through a second focus of the projector lens, and a third reflective surface formed as a plane connected to the fore-end edge to extend toward the back of the fore-end edge.
As shown in FIG. 3 of Japanese Patent Application Laid-Open No. 2003-317513, the first reflective surface reflects emitted light from the LED to focus the light on a front/back position of the vicinity of the second focus of the back side of the projector lens within the vertical cross section. The reflected light, which has been reflected to the front side of the second focus and has passed through the fore-end edge of the light control member, is emitted from the projector lens to the front side of the vehicle to form a low-beam light distribution pattern including predetermined horizontal and inclined cutoff lines. Meanwhile, in the light source unit disclosed in Japanese Patent Application Laid-Open No. 2003-317513, light which has been reflected to the back side of the second focus and has been blocked by the fore-end edge of the light control member is also re-reflected upwardly by the third reflective surface to enter into the projector lens, and the light forms the low-beam light distribution pattern together with the light having passed through the fore-end edge of the light control member, minimizing the loss of light.
Since the lamp unit disclosed in Japanese Patent Application Laid-Open No. 2003-317513 re-reflects the light having been blocked by the light control member (light blocking shade) by the third reflective surface to use the re-reflected light for the low-beam light distribution pattern, the loss of light can be reduced to make the low-beam light distribution pattern brighter. Meanwhile, according to checking the light distribution pattern of Japanese Patent Application Laid-Open No. 2003-317513, it has been found out that since the third reflective surface is a horizontal surface in the lamp unit, the re-reflected light is intensively reflected at an upper area of the low-beam light distribution pattern.
With respect to the light flux entering into the third reflective surface to be focused in the vertical cross section, since the third reflective surface is a horizontal plane, the reflection angle of the light having been re-reflected by the fore-end edge of the light control member (hereinafter, simply referred to as a re-reflected beam) is at the maximum, and the reflection angle decreases as the reflection position of the re-reflected beam approaches the back. Therefore, the light flux entering into the third reflective surface is not re-reflected toward a further upper side as compared to the re-reflected light by the fore-end edge of the light control member. Meanwhile, since an image of the light flux by the third reflective surface is turned upside down by the projector lens, the re-reflected beam by the fore-end edge of the light control member is irradiated at the lowest position on the image of the light flux, and the re-reflected light flux is irradiated onto the further upper side as compared to the re-reflected beam by the fore-end edge. Therefore, in the lamp unit disclosed in Japanese Patent Application Laid-Open No. 2003-317513, it is considered that the beam re-reflected by the fore-end edge of the light control member is irradiated on the upper area of the low-beam light distribution pattern, and the light flux of the re-reflected light is intensively reflected to the upper area of the low-beam light distribution pattern.
In a case where the light flux of the re-reflected light by the third reflective surface is intensively reflected to the upper area of the low-beam light distribution pattern, the upper area of the light distribution pattern close to the cutoff line become relatively brighter, while the lower area of the light distribution pattern which has not been subject to light supplement looks darker. Therefore, there exists a large difference in brightness between the upper and lower areas of the low-beam light distribution pattern. The low-beam light distribution pattern having the large difference in brightness as described above makes it difficult for a driver to see the right front side of the low-beam irradiation area, causing a visibility problem for the driver.